Effect of low-dose dexmedetomidine to prolong spinal anesthesia in elderly patients: a prospective randomized controlled study

The Takeaway

Low-dose dexmedetomidine effectively enhances spinal anesthesia in elderly patients, potentially improving surgical outcomes and patient comfort.

Key findings:

• Single dose of 0.4 mcg/kg IV dexmedetomidine prolongs spinal anesthesia
• Significantly extended sensory block duration
• Improved postoperative analgesia

Study details:

• Prospective randomized controlled trial
• Elderly patients undergoing spinal anesthesia
• Compared dexmedetomidine to control group

Physiology Refresh

Precedex is a highly selective alpha-2 adrenergic receptor agonist that works primarily through the following mechanisms:

Primary Mechanism: Alpha-2 Adrenergic Receptor Activation

Dexmedetomidine binds with high selectivity to alpha-2 receptors (particularly the alpha-2A subtype) with an alpha-2 selectivity ratio of approximately 1600:1. This is significantly higher than clonidine, another alpha-2 agonist.

Central Nervous System Effects

1. Locus Coeruleus: The primary site of action is the locus coeruleus in the brainstem, where dexmedetomidine inhibits norepinephrine release by presynaptic activation of alpha-2 receptors.
2. Sedation: Unlike traditional sedatives (benzodiazepines, propofol), dexmedetomidine produces a unique "arousable sedation" resembling natural sleep. Patients can be easily awakened and remain cooperative even during sedation.
3. Anxiolysis: Reduces anxiety without significant respiratory depression.

Analgesic Effects

Dexmedetomidine produces analgesia through:

• Inhibition of substance P release in the dorsal horn of the spinal cord
• Activation of alpha-2 receptors in the spinal cord
• Modulation of descending noradrenergic pathways

The analgesic effect is moderate but can significantly reduce opioid requirements.

Sympatholytic Effects

1. Hemodynamic effects: Produces a biphasic cardiovascular response:
   • Initial transient hypertension (due to peripheral alpha-2B receptor activation)
   • Followed by hypotension and bradycardia (due to central sympatholytic effects)
2. Reduces plasma catecholamine levels by up to 90%

Other Physiological Effects

1. Minimal respiratory depression: Unlike opioids and other sedatives, dexmedetomidine preserves respiratory drive even at higher doses.
2. Anti-shivering properties: Useful for hypothermia management and post-anesthetic shivering.
3. Neuroprotective potential: May reduce ischemic injury through several mechanisms including modulation of apoptosis.
4. Organ-protective effects: Some evidence suggests protective effects on heart, kidney, and brain tissue, likely through anti-inflammatory and anti-oxidant properties.

Excerpts

Kaya et al. revealed that intravenous (IV) dexmedetomidine at a dosage of 0.5 µg/kg in patients undergoing TURP extended spinal anesthesia, delayed the first analgesic request, and reduced postoperative pain medication demand.

The ED95, ensuring adequate sedation within 20 min for elderly patients, was 0.4 µg/kg.

The present study showed a significant prolongation of the regression of two dermatomes with single doses of dexmedetomidine (0.4 µg/kg) without increasing the incidence of bradycardia and hypotension.

From our study, no excessive sedation or serious respiratory complications were reported based on intraoperative or PACU data.

Abstract

Background

Spinal anesthesia for transurethral resection of the prostate (TURP) has a short duration, which poses challenges for postoperative pain management. The present study aimed to investigate the effects of intravenous (IV) dexmedetomidine at a dosage of 0.4 µg/kg in prolonging the duration of spinal anesthesia and minimizing postoperative pain in elderly patients undergoing TURP.

Methods

This prospective randomized controlled trial enrolled 38 patients aged 60-80 years who underwent elective TURP with spinal anesthesia. The patients were randomly assigned to two treatment groups: Group D received IV 0.4 µg/kg dexmedetomidine, whereas Group C received IV normal saline after spinal anesthesia administration. The primary outcome was the time to 2-dermatome regression.

Results

The 2-dermatome regression time was longer in Group D than in Group C (104.44 ± 16.97 min vs. 80.63 ± 15.59 min, p < 0.05). The peak sensory block levels were significantly higher in Group D [T7 (T6-T8)] than in Group C [T10 (T7-T10)] (p = 0.017). The incidence of hypotension and bradycardia and postoperative pain at 0, 6, 12, and 24 h were not different between two groups.

Conclusion:

Intravenous dexmedetomidine at a dosage of 0.4 µg/kg significantly prolongs the duration of spinal sensory blockade. Although postoperative analgesia was not different, it provided hemodynamic stability without increasing the side effects.

Citation

Sangkum L, Termpornlert S, Tunprasit C, Rathanasutthajohn C, Komonhirun R, Dusitkasem S. Effect of low-dose dexmedetomidine to prolong spinal anesthesia in elderly patients: a prospective randomized controlled study. BMC Anesthesiol. 2024 Nov 26;24(1):427. doi: 10.1186/s12871-024-02815-z. PMID: 39592975; PMCID: PMC11590567.

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